Since a switch is designed to handle multiple connections it shouldn't be "the" bottleneck. However, if you are using something like a home based 4 port switch that has limited bandwidth to your DSL or Cable modem bonding isn't going to help you much because you'll still be limited to that link's bandwidth.
However, in a typical data center, bonding can help because the backbone is capable of much more.
Also, there are other bonding modes that have nothing to do with speed but rather stability We use bonding for two NICs so that if one NIC or port on the switch goes down we still have an interconnect for our cluster because the other one is still up. Interestingly this is for Oracle RAC cluster and the bonded NICs go through a switch port because crossover cables between the hosts (which would have been easy for us) don't have enough latency so can cause a problem.
Last edited by MensaWater; 09-01-2010 at 08:36 AM.